(347g) Shape-Specific FePt Nanomagnets for Spin Torque Memory Devices

Morphological control of inorganic nanocrystals has become increasingly important, as many of their physical and chemical properties are highly shape dependent. FePt nanocrystals have potential as advanced magnetic materials for ultrahigh-density recording media and high-performance permanent magnets. This is based on their high uniaxial magnetocrystalline anisotropy. These nanocrystals were synthesized by simultaneous reduction of platinum acetylacetonate (Pt (acac)2) and thermal decomposition of iron pentacarbonyl (Fe (CO)5) in properly chosen solvents/surfactants proportions for rational design of their shape and magnetic properties. The as-synthesized nanocrystals, having chemically disordered fcc structure, are found to be superparamagnetic at room temperature and their coercive fields are governed by their morphology. The chemically ordered L10 structure, induced upon heat treatments, exhibits hard magnetic properties with enhanced coercivity. Monolayer assemblies of the as-synthesized FePt nanostructures with different shapes, including nanorods, oval-shaped particles and spherical particles have been synthesized and characterized by transmission electron microscopy (TEM). This work determined that not only the molar ratio of surfactants but also the sequence of the addition of the surfactants and metal precursors and the temperature reaction affect the shape of FePt nanoparticles. The hysteresis loops of randomly oriented assemblies of nanowires, obloids, and spherical nanoparticles as-synthesized and annealed were observed during magnetometry measurements. Also, in this paper focus on determining the temperature dependence of the magnetization for the fabricated FePt colloidal assemblies will be discussed.